The present invention relates to an illumination apparatus that irradiates light from a light source, and an image-taking apparatus having the illumination apparatus.
An illumination apparatus for use with a conventional image-taking apparatus, such as a camera, includes a light source, a reflector and an optical element, such as a Fresnel lens, that are used to introduce the light from the light source to a front or subject side.
A variety of proposals have been made to such an illumination apparatus so as to reduce its size and efficiently condense the light that is emitted from the light source in various directions, into a necessary irradiation angle of view. See Japanese Utility-Model Application, Publication No. 2-138733 and Japanese Patent Application, Publication No. 7-270867.
For example, the illumination apparatus shown in FIG. 6 includes a 10 having a reflective surface, and an optical element 11 that has an incident surface and an exit surface. The incident surface is a positive refractive part that provides a positive refractive power to the light near an irradiation optical axis AXL among the lights irradiated from a light source 9 to a subject side. The exit surface exits the light from the incident surface. The reflective surface of the reflector 10 reflects toward the subject the light exited from the light source 9 at an angle apart from the irradiation optical axis AXL. Due to the reflective surface, rays approximately perpendicular to the irradiation optical axis AXL among the lights emitted from the light source 9 at a predetermined angle or larger from the irradiation optical axis AXL are incident upon the optical element 11, and then exited from the optical element 11 as exit rays at necessary angles to the irradiation optical axis AXL. The rays reflected on the tip of the reflective surface and then exited from the optical element 11 are approximately parallel to the irradiation optical axis AXL.
This illumination apparatus is a small and efficient one, because it can be made small in the height and length directions.
Along with the recent diversified camera body designs, many cameras' exterior members have complicated curved surfaces, e.g., gradually changing curvatures. When the camera body's exterior shape is configured by a complicated curved surface, it is preferable for an attractive appearance that an illumination optical system's surface that is closest to the light irradiation or subject side also has a stepless curved surface adjusted to the camera body's shape.
However, the conventional camera having the illumination optical system is problematic in poor design freedom of the camera body.
For example, the illumination apparatus disclosed in Utility-Model Application, Publication No. 2-138733 decenters a surface of the Fresnel lens on the subject or light irradiation side. However, as the rotationally central axis of the Fresnel lens is perpendicular to the Fresnel surface similar to prior art, the illumination optical system disclosed in this reference has a limit to correct a parallax with an optical axis of the image-taking lens and cannot increase the design freedom of the camera body.
In the illumination apparatus disclosed in Japanese Patent Application, Publication No. 7-270867, the Fresnel lens surface on the subject or light irradiation side is oblique to the optical axis of the image-taking lens. The Fresnel lens surface on the light source side is composed of cylindrical surfaces of plural Fresnel elements each having a cylindrical surface. At least one of the Fresnel angle of each Fresnel element and the cylindrical surface shape vary among the Fresnel elements in accordance with the inclination of the Fresnel lens surface on the light irradiation side to the optical axis of the image-taking lens, and correct the light bias caused by an inclination of the Fresnel lens's surface on the illumination range side.
Nevertheless, the illumination optical system in this reference discusses only the Fresnel lens shape and is silent of a reflector shape.
When the optical element 11 in the illumination apparatus shown in FIG. 6 is replaced with an optical element 12 having an exit surface that is designed to have a large curvature R as shown in FIG. 7, part of the light reflected by the reflector 10 among the lights from the light source 9 is totally reflected on the exit surface of the optical element 12, does not reach the subject, and can lower the light intensity on the subject. The exited light spreads little, converges in a certain direction, and also causes the non-uniform light distribution.